This invention relates to an improved apparatus and method for in vivo monitoring of visually accessible surfaces of the body. Surfaces, such as the skin are directly accessible, while other surfaces, such as the cervix, the retina, and the vascular endothelium require an optical apparatus to be visibly accessible.
Systems identification is the engineering method whereby parameters of a system, in this case a biological surface, defined by its optical properties, are "identified"--that is quantitatively estimated--using data derived from input and/or output signals of the system. The spatial, temporal, and spectral distributions of light stimulating a biological surface may be considered the input signals to the system, and the spatial, temporal, and spectral distributions of light reflected by or emitted from the system may be considered the output signals of the system.
Computer vision refers to engineering methods whereby images are analyzed, using tools including image processing, quantitative feature extraction, and decision theory, to interpret the contents of the images. Thus, by combining systems identification with computer vision, images of a biological surface, obtained under various lighting and/or viewing conditions, may be used to provide parameters describing features of surface structures or processes.
An example of a surface commonly monitored for abnormalities is the skin. Skin cancer incidence has increased markedly in recent years. Present clinical methods of screening and monitoring cutaneous surfaces for premalignant features include, qualitative assessment, of gross visual features of dysplasia or malignancy (such as asymmetry, border irregularity, color variability, diameter and elevation of skin lesions), and sequential examination, relying on the physician's memory, written descriptions, sketches, and visual inspection of conventional analog photographs, to assist in deciding if a surface lesion is new or has features which have changed. Patients with dysplastic nevi syndrome may have hundreds of pigmented skin lesions which need to be monitored for signs of cancer. A system which systematically (1) monitors the number of lesions and their positions on the body surface, and (2) quantifies morphologic and spectral features of such lesions would provide a useful tool for improving management of this potentially deadly disease.
Another surface routinely monitored for abnormalities is the cervix. Cancer of the cervix is a common cancer in women. Digital colposcopy with simple image enhancement has been shown, anecdotally, to detect premalignant cervical abnormalities in cases where the standard screening test, the Papaniocoloaou smear, was falsely negative.
Another example of a surface where visual examination is essential in order to detect abnormalities or changes is the retina. Retinal imaging is an important method for detecting, monitoring, and guiding therapy for clinical conditions which may lead to blindness. Photogrammetric methods for obtaining three dimensional measurements of retinal structures from analog stereo photographs and simple digital methods for two-dimensional imaging of retinal features are presently in the vanguard of methods used to monitor certain retinal features.
The vascular endothelium, however is the anatomic surface responsible for the majority of deaths in this country (i.e. due to myocardial infarction). The optical apparatus necessary to view it has recently become available in the form of angioscopic catheters, yet no systematic method for analyzing and utilizing images of this surface has been developed.
For each of these visually accessible anatomic surfaces, a coherent synthesis of appropriate digital methods for systems identification and computer vision would improve the detection and monitoring of abnormalities, before, during, and after therapy.